1. Field of the Invention
The present invention generally relates to a wind turbine with a self-contained power system and, more particularly, to a wind turbine with a self-contained power system comprising an auxiliary generator with a winding disposed on the hub of the wind turbine while the magnetic poles of the auxiliary generator are disposed at a mechanism which is rotating relatively to the rotor. Thereby, a back electromotive force (emf) is generated in the winding due to the relative motion of the winding with respect to the magnetic poles as the rotor is rotating, and consequently the self-contained power system generates electricity to provide the power for tuning the blades' pitch angles.
2. Description of the Prior Art
For a large-size wind turbine, the output power can be adjusted by the blade by means of passive stall, active stall and pitch regulation. Pitch regulation used with a variable-speed generator exhibits the best controllability and is widely used in large-size wind turbines.
Pitch regulation can use hydraulic or electric pitch drives. However, with the increase of the output power of a large-size wind turbine, the electric pitch drive has advantages over the hydraulic pitch drive because the former has more flexibility in power adjustment without leakage problem.
Please refer to FIG. 1, which is a schematic diagram of a prevailing pitch regulated wind turbine. The wind turbine 10 comprises a nacelle 12 disposed on a tower 11. A rotor 13 is connected to the nacelle 12. The rotor 13 has a plurality of blades 132 disposed around the circumference of a hub 131. The nacelle 12 includes a gearbox 15 and a generator 17 and other components such as a power converter and a wind turbine controller (not shown). Via the gearbox 15, the variable-speed generator 17 is indirectly coupled to the hub 131 and is controlled by the power converter and the wind turbine controller. Each of the blades 132 is connected to a pitch drive 133 residing inside the hub 131. The pitch drive 133 generally comprises at least a gear set, a motor and a driver (not shown) so as to regulate the pitch angle of the blade 132 and adjust the wind power collected by the blades 132. The hub 131 is connected to the gearbox 15 by way of a shaft 14 disposed in the nacelle 12. As the rotor 13 is a rotating structure, the pitch drive 133 in the hub 131 cannot be rigidly interfaced with the nacelle 12 using fixed connecting wires. Therefore, a slip ring 16 is required on the shaft 14 for connecting the hub 131 and the nacelle 12, so the transmission line 163 can be disposed unrestrictedly. Moreover, a back-up power supply 134 is installed in the hub 131 so as to provide sufficient power for the pitch drives 133 when the power system is at faulty condition.
Accordingly, the large-sized wind turbine relies on the power system or the back-up power supply even though it generates considerable amount of electricity. In other words, the large-sized wind turbine still replies on another power supply even though it is a power generator. On the other hand, the power provided from the slip ring 16 increases with the output power of the wind turbine, and therefore the power required by the pitch drive increases. The specification of the slip ring has to be adjusted according to the power rating and maintenance so as to meet the requirements in reliability of the wind turbine.
Therefore, it is crucial to provide a wind turbine with a self-contained power system so as to enhance the standalone operation ability of the wind turbine and reduce the capacity of the back-up power supply.